Physicists describe the phenomenon of "action at a
distance" as the perceived effects on an object without there being
any form of touch to transfer energy by another object. It is the
interaction between two objects not connected to each other. Albert
Einstein described the phenomenon as "spooky action at a
distance" and it has fascinated us since Roald Dahl's Matilda
made the Cheerios box to tip over with just her mind.

Now a team of physicists have figured out a method to rigorously
test if pairs of photons&nbsp;- particles of light
-&nbsp;display this "spooky action at a distance" effect
even under adverse conditions outside a lab setting. This could greatly
improve internet security, data security concerns and privacy in general
by helping in detecting attacks by hackers. The&nbsp;study was
conducted by a&nbsp;team from Griffith University,&nbsp;Centre
for Quantum Dynamics in Australia.

As photons travel through an optic fiber medium carrying
information, some of them gets&nbsp;scattered. As they travel
through longer distances, more get lost.&nbsp;Information sent via
photons are lost during high-speed transfer. These photons can then be
easily be intercepted and the data that was sent can easily be decoded
by hackers.

"As the length of quantum channel grows, less and less photons
successfully pass through the link, because no material is perfectly
transparent and absorption and scattering take their toll," said
team leader Professor Geoff Pryde&nbsp;in a
(https://app.secure.griffith.edu.au/news/2018/01/06/quantum-spooky-action-at-a-distance-becoming-practical/) statement .&nbsp;

An effect known as quantum nonlocality - two quantum systems
(computers) linked together - is seen as the integral property that
helps gauge security during data transfer between two computers. It
involves checking the data sent and received to check if the information
reach the destination.

Two 'entangled' photons are used in data transfer systems
that are linked together between two locations where the transfer needs
to occur. These pair of photons are "entangled" so that
measuring one determines the properties of its twin.

This means that even when interactions between two nonlocal
(entangled) photons are verified, it does not account for many of the
photons lost by absorption or scattering as they travel from source to
destination through an optical fiber channel. It just shows the
successful information relay between the source and destination which
confirm the transfer but the real question is, was it secure?&nbsp;

This is a problem for existing quantum nonlocality verification
techniques in gauging security concerns. Every photon lost makes it
easier for the eavesdropper to break the security by gaining knowledge
of the nature of the photons and mimicking it. Here is where
entanglement kicks in.

If scientists can test entanglement when there is a data loss, it
can easily tell them if there is a difference in the information between
two points and if photons have been lost. But, it is not so easy.
Developing a method to test entanglement in presence of loss has been a
challenge for the scientific community for quite some time.

To test the entangled photons, the team came up with an
approach&nbsp;- called&nbsp;quantum teleportation
-&nbsp;which helped them study quantum entanglement even in
high-loss systems.

Dr Morgan Weston, first author of the study said the team chose few
photons that survived the high-loss channel and reached the destination
without getting scattered. These photons were then
"teleported" into another clean and efficient&nbsp;quantum
channel where they were subjected to the usual quantum steering tests to
determine the interaction or entanglement even when losses were suffered
in the earlier system.

"There, the chosen verification test, called quantum steering,
could be done without any problem," Weston said.

"Our scheme records an additional signal that lets us know if
the light particle has made it through the transmission channel. This
means that the failed distribution events can be excluded up front,
allowing the communication to be implemented securely even in the
presence of very high loss," she added.

The teleportation step involves the use of high-quality photon
pairs on its own. These extra photon pairs have to be generated and
detected with extremely high efficiency, in order to compensate for the
effect of the lengthy transmission line where the researchers saw
losses. But putting them in an ideal system helped the researchers study
quantum entanglement.

With this method, the team were able to test channels with photon
absorption equivalent to about 80 km of telecommunications optical
fiber.&nbsp;The (http://advances.sciencemag.org/content/4/1/e1701230) study was published in the journal Science Advances on Jan. 5.

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